Calculating Real Home Field Advantage

Quite often in the baseball betting world you’ll realize that home teams are significant favorites over road teams. However, on any given day on the diamond when there are a full slate of 15 games, you’ll see a handful of upsets, and perhaps a ton of upsets. Unlike football, where home field advantage is assigned at anywhere from 2 ½- through 3 ½-points, coming up with a legitimate home field advantage in baseball is tough, and it isn’t something that is easily discernible.

Analyzing Home Team Records

The easiest way to go about this task is to try to figure out what a team does at home in relation to what it does on the road every single season. In the 2012 campaign, there were only four teams (Boston, Minnesota, New York (N), and Philadelphia) that posted better records on the road than they did on the road. Of those, only the Minnesota Twins were more than one-game better away from home than they were at their home ballpark.

An easy study to try to figure out the fair MLB moneyline value is to simply figure out what percentage of the games were won by home teams over a given period of time.

2012

Home Teams: 1295-1135 (53.29%)
Road Teams: 1135-1295 (46.71%)

2011

Home Teams: 1277-1152 (52.57%)
Road Teams: 1152-1277 (47.43%)

2010

Home Teams: 1359-1071 (55.93%)
Road Teams: 1071-1359 (44.07%)

History will tell you that the winning percentages for home teams were actually low in 2011 and 2012 and a bit high in 2010. According to Baseball Reference, there hasn’t been a single season since 1920 in which the road team has won more games than the home team, and the home team winning percentage ranges anywhere from 51.0% up to 58.2% depending upon the season. If we just look at games played since 2000 though, the range is significantly smaller from 52.6% up to that 55.93% we saw in 2010.

If you were to carry back the data of the home team’s winning percentage to 2006, you would see that home teams have gone 9261-7747, or a winning percentage of 54.45%. Going back even more to 2000, that winning percentage is 54.48%, and the home team winning percentage dating back to 1980 was 54.57%. The numbers are remarkably consistent.

Coming Up With the Real Home Field Advantage

Now that I have established what the winning percentage is for home teams, I can easily go back and assess what that translates into in terms of betting lines.

Using our Odds Converter, we could easily plug into the Implied Probability section 54.45% to see that the fair moneyline price is right around -120. The fair moneyline price for road teams is the exact opposite at +120. Throw in the vig that an average sportsbook collects on baseball games, and the home team should be -125, while the road team should be +115 in the event that two perfectly evenly matched teams played against each other.

Calculating a Fair Betting Line

Of course, this doesn’t mean that every home team in baseball should be -120. In actuality, the Implied Probability number is of far more use to us. Your first task should be to figure out how often Team A is going to beat Team B.

Example: Say that theoretically, you handicap the New York Yankees to be able to beat the Seattle Mariners 62% of the time on a neutral field. That means that right off the bat, the Bronx Bombers should be -163 to win the game. Consequently, Seattle should be +163 in that situation.

How to Do the Calculation
Now, we have to factor in the home field advantage. Everything basically has to be multiplied by the value of home field advantage to come up with a betting line. If home teams win 54.45% of the time, road teams win 45.55% of the time, and games played on a neutral field are legitimately 50/50 tossups, the difference is 4.45%. This is the fair home field advantage factor.

Let’s go back to my example of the Mariners and the Yankees. If the Yankees are playing at home, that means that I need to multiply the 62% winning percentage by the home field advantage factor (4.45%). Here’s the math…

Going back to our odds converter, our Implied Probability of the Yankees winning in this scenario is 64.79%, which would translate to a -184 betting line. Anything better than -184, and you have the advantage on your side by betting the Yankees. Anything worse than -184, and you should stay away.

Consequently, when you’re calculating the disadvantage of playing on the road, you just have to subtract the home field advantage factor instead of adding it.